This study is designed to obtain information applicable to developing a detailed explanation of the molecular processes involved in photoreceptor function. Visual pigments represent a class of intrinsic membrane proteins, whose retinal chromophore serves as a receptor site for photons. Of particular interest in this study is the transduction step, in which a photon, absorbed by rhodopsin, results in a hyperpolarization of the rod outer segment plasma membrane. A major goal of this research is to elucidate the mode of coupling of the photochemical event with the subsequent membrane hyperpolarization. This will involve a study of the role of rhodopsin as either a pore or transport protein, or alternatively as an initiator of some enzymatic sequence, such as the activation of the ROS cGMP phosphodiesterase. An additional goal of this research is to delineate the role of the membrane microenvironment in modulating the transduction process. Of particular interest is the role of the uniquely high level of 22:6 acyl side chain in ROS dish phospholipid side chains. By this approach the dependence of the transduction process on membrane microenvironment and the role of rhodopsin in this process can be elucidated. Efforts will be made to determine if unique functional domains exist in the structure of rhodopsin.